An inhaler of the above general kind has several advantages in comparison to standard multiple powder inhalers containing a large number of doses in a store for the powdered drug from which the powder is fed to a dispensing station.
The drug thus can be protected against moisture in a simple and efficient way since each individual dose of the drug can be tightly enclosed and sealed between the cover strip and the elongate carrier. The utilization of the drug is high since there is no store that may have to be overfilled to ensure definitely that there is drug available as long as the dose counter indicates there should be. The number of doses can be varied in a simple way by cutting different lengths from a continuous elongate carrier. It is easy to arrange a simple counting device indicating the number of doses used or remaining. A simple indication that all doses have been used up may be obtained merely by the fact that the carrier is used up, which is easy to determine. The device may finally also be designed to be reusable several times which would make the device cheap in use, since it is easy for the patient to refill the device in a safe way without any risk of exposing the drug to moisture.
A further advantage of using an elongate carrier is that the counting device may be dispensed with entirely if each dose is numbered, i.e. a numeral is assigned to each dose, the numerals being consecutively visible through an opening in the housing. Preferably the doses are numbered backwards with the highest numeral assigned to the first dose. In this way a simple way of indicating the number of doses remaining may be obtained without any need for a counting mechanism.
An inhaler of the kind as described in the introduction above and in the preamble of the main claim is for instance disclosed in GB-A-2 242 134. This prior art device utilizes the depressions or cavities in an elongated carrier in cooperation with indexing or registering means in order to control that the depressions containing the doses are positioned correctly in the dispensing station. In one embodiment the device is provided with a spool taking up the cover strip (the indexing means are here engaging the depressions which are used to move the carrier). However, since the diameter of the spool taking up the cover strip will vary in dependence of the amount of strip wound on the spool, the winding speed of the cover strip consequently also will vary, whereas the movement of the carrier will not. To compensate for this, the spool taking up the cover strip has been provided with a rather complicated friction coupling allowing the take-up spool to slip in relation to the movement of the elongated carrier.
In an alternative embodiment which is suggested, but not described in detail, the distances between the depressions in the elongate carrier have been varied in order to compensate for the above effect, which however complicates the manufacturing and filling process for the elongate carrier. Further, the number of doses generally cannot easily be varied by cutting a long prefabricated carrier part into pieces having different lengths.
In both cases the elongate carrier (and the depressions in particular) must be comparatively stiff to permit the use of the depressions as actuating means in conjunction with indexing or registering means. This may be undesirable in some applications. The use of the depressions in combination with the indexing means also results in limitations on the size of the depressions since the depressions, apart from the stiffness mentioned above, also have to have a minimum size in order not to slip through the indexing or registering means. This means that the doses also have to have a minimum size.
Some other related prior art devices are disclosed in for instance WO 90/13327, WO 90/13328, and EP-A1-0 469 814.